An exemplary embodiment of this application relates to an ink jet printer having a transfixing station with multiple transfixing operating modes to enable printing of both simplex and duplex prints with increased overall printing speed. More particularly, the exemplary embodiment relates to an ink jet printer having a print head that ejects ink droplets onto a moving intermediate surface coated with a release agent to produce an ink image thereon and a transfixing station where the printed ink images are transferred onto a recording medium. The transfixing station includes a movable transfixing roll that is moved into and out of contact with the intermediate surface to form a transfixing nip using different timing modes for simplex and duplex prints.
Droplet-on-demand ink jet printing systems eject ink droplets from print head nozzles in response to pressure pulses generated within the print head by either piezoelectric devices or thermal transducers, such as resistors. The ejected ink droplets are propelled to specific locations on a recording medium, commonly referred to as pixels, where each ink droplet forms a spot on the recording medium. The print heads have droplet ejecting nozzles and a plurality of ink containing channels, usually one channel for each nozzle, which interconnect an ink reservoir in the print head with the nozzles.
In a typical piezoelectric ink jet printing system, the pressure pulses that eject liquid ink droplets are produced by applying an electric pulse to the piezoelectric devices, one of which is typically located within each one of the ink channels. Each piezoelectric device is individually addressable to cause it to bend or deform and pressurize the volume of liquid ink in contact therewith. As a voltage pulse is applied to a selected piezoelectric device, a quantity of ink is displaced from the ink channel and a droplet of ink is mechanically ejected from the nozzle associated with each piezoelectric device. Just as in thermal ink jet printing, the ejected droplets are propelled to pixel targets on a recording medium to form image information thereon. The respective channels from which the ink droplets were ejected are refilled by capillary action from an ink supply. For an example of a piezoelectric ink jet printer, refer to U.S. Pat. No. 3,946,398.
The problem of ink drying time and paper cockling are widely recognized issues when printing high coverage areas with aqueous based inks, particularly when printing color images. The problem of drying time and paper cockling is substantially reduced when solid ink printers are used and their print heads eject droplets of melted ink onto the recording medium, where the melted ink droplets solidify immediately. Further improvement in the drying time and cockling problem is obtained when the print head ejects droplets of melted ink onto an intermediate surface, such as, for example, a drum, that has a release agent coating thereon. Once the image is formed on the intermediate surface, the image is then transferred to a recording medium, such as paper. The transfer is generally conducted in a nip formed by the rotating intermediate transfer drum surface and a rotatable pressure roll. The pressure roll may be heated or the recording medium may be pre-heated prior to entry in the transfixing nip. As a sheet of paper is transported through the nip, the fully formed image is transferred from the intermediate transfer drum surface to the sheet of paper and concurrently fixed thereon. This transfer technique of using the combination of heat and pressure at a nip to transfer and fix the image to a recording medium passing through the nip is usually referred to as “transfixing,” a well known technology.
Ink jet printers are capable of producing either simplex or duplex prints. By simplex prints, it is meant that the image is on only one side of the recording medium. By contrast, duplex prints have an image on both sides of the recording medium; i.e., the front side and back side of the recording medium. A problem arises, if excessive release oil is present on the transfixing roll, when duplex prints are to be produced. When the first side of a recording medium has an image transfixed to it by the transfixing roll from the intermediate transfer drum, the second or back side of the recording medium may have some oil transferred to it. To complete the duplex print, it is inverted and returned through the transfixing nip to transfix the second image on the back side of the recording medium. Release oil on the side of the recording medium that is to have an image transferred to it would cause reduced transfer efficiency. Therefore, it is one aim of this application to prevent or reduce the application of release oil onto the second side of duplex prints by the transfixing roll at the transfixing station.
Some release agent, such as, for example, silicon oil, is applied to the transfixing pressure roll, as well as the surface of the intermediate transfer drum, because zero oil on the transfixing pressure roll also causes problems. However, only a small amount of release oil is applied to the pressure roll to make sure that a very small oil level is present. Permitting some excess release oil on the transfixing pressure roll to be transferred onto the backside of a simplex print is not a problem, but to do so for a duplex print would cause a duplex transfer latitude problem.
Some conventional solid ink jet printers utilize a process timing that does not allow the transfixing roll to become excessively oiled, but such process timing limits printing speed and thus impacts printer productivity. In one known solid ink jet printer, the transfixing roll is spaced from the intermediate transfer drum and is moved to produce a nip with the intermediate transfer drum only after the intermediate transfer drum is stopped with the top of the image thereon registered at the nip location. Before the nip is formed, the leading edge of a recording medium is transported into the transfixing nip region. Therefore, the transfixing roll engages the leading edge of the recording medium and sandwiches it between the transfixing roll and the intermediate transfer drum, so that the transfixing roll does not engage or contact the oil coated intermediate transfer drum surface when a transfixing nip is formed. Once the nip is formed, the transfixing roll and intermediate transfer drum are rotated to transport the recording medium through the transfixing nip and concomitantly transfixing the image to it. Conversely, the transfixing roll is disengaged from the trailing edge of the recording medium before the recording medium leaves the transfixing nip. Because of this process timing, the transfixing roll never contacts the release oil coated intermediate transfer drum surface, and hence is kept sufficiently dry of oil. Such a timing process sequence is sometimes referred to as a ‘stop edge’ process. Clearly, stop edge timing for the transfixing roll impacts printer productivity.
To increase the printing speed of the ink jet printer and therefore the printer's productivity, there is a need for faster transfixing of simplex prints, while concurrently preventing excessive release oil from getting on the transfixing roll from the intermediate transfer drum during the transfixing of duplex prints. The prior art has not done this in a cost effective manner. Examples of ink jet printers having an intermediate transfer drum from which printed images are transferred to a recording medium at a transfixing station are disclosed below.
U.S. Pat. No. 5,099,256 discloses a thermal ink jet printer having a translatable multicolor print head and a rotatable intermediate transfer drum with a film forming silicone polymer layer on the outer surface thereof. The drum surface is heated to dehydrate the aqueous based ink droplets deposited thereon from the print head at a first location. The drum is rotated and the dehydrated droplets are transferred from the drum to a recording medium at a transfer station positioned adjacent the drum at a second location.
U.S. patent application Ser. No. 11/040,040, filed Jan. 21, 2005, discloses an ink jet printer having a print head that moves in a two dimensional direction across the surface of a moving intermediate transfer drum or belt. During the printing process, the print head is concurrently moved in a first direction at a velocity equal to the velocity and direction of the intermediate surface and in a second direction that is perpendicular to the first direction. This two dimensional movement of the print head causes the ink droplets to print swaths of information across the intermediate surface that are perpendicular to the first direction. Downstream from the print head, the printed information is transferred and fixed to a recording medium as it is transported through the transfixing nip at the transfixing station.
U.S. patent application Ser. No. 10/974,768, filed Oct. 28, 2004, discloses an ink jet printer having a print head, intermediate transfer drum, and transfixing station. Test images are formed on the interdocument space or blank portions of the intermediate transfer drum by those nozzles of the print head that are most likely to be defective. Thus, the time and ink required to form the test images with nozzles unlikely to be defective is not wasted. The test images printed by the potentially defective nozzles are tested using an image sensor.
U.S. Pat. No. 5,389,958 discloses a method and apparatus for transferring an ink image from an intermediate surface to a final receiving substrate. A layer of sacrificial liquid is applied to the intermediate surface and a phase change ink is deposited on the liquid layer. The ink image is then contact transferred to a final receiving substrate.
U.S. Pat. No. 6,196,675 discloses an apparatus and method for image fusing in an ink jet printing system. The ink image is transferred to a final receiving substrate by passing the substrate through a transfer nip. The substrate and ink image are then passed through a fusing nip that fuses the ink image into the final receiving substrate. Utilizing separate image transfer and image fusing operations allows improved image fusing and faster print speeds.
U.S. Pat. No. 6,494,570 discloses a method for transfer and fusing in an ink jet printer. In the method, an ink image is formed on an intermediate transfer surface, a final receiving substrate is passed through a first nip, a first pressure is exerted on the final receiving substrate in the first nip to transfer the ink image from the intermediate transfer surface to the final receiving substrate, the final receiving substrate is then passed through a second nip where a second pressure and temperature is exerted on the final receiving substrate to fuse the ink image into the final receiving substrate.